Fast-cure resin formulations with consistent handling characteristics

ABSTRACT

The present invention relates to rapid-curing resin formulations as well as fiber-reinforced composite materials comprising the same and their use in the manufacture of molded articles, particularly where the manufacturing process requires high throughput and where resin formulations having consistent handling characteristics (e.g., tack and flexibility) would be preferable across normal to elevated laminating environments (as defined by temperatures between 20° C. and 60° C.). The present invention further relates to a manufacturing process for preparing an article, particularly a molded article, from a fiber-reinforced composite material comprising a rapid-curing resin formulation.

RELATED APPLICATIONS

This application claims priority to U.S. provisional application No.62/637,362, filed Mar. 1, 2018. The entire contents of this applicationis explicitly incorporated herein by this reference.

BACKGROUND

A fibrous layer of material (e.g., carbon fiber or glass fiber, amongnumerous others), or a fabric made from such materials, which has beenpartially or fully impregnated with a resin, such as a curable resin isknown as a pre-preg. Fiber-reinforced resins, including pre-pregs, areused to form cured composite articles. Multilayers of fiberreinforcement (e.g., in a pre-preg) and resins may be laid up in a mold,and then cured to form a cured composite article. Such cured compositearticles can be used, for example in automobile, aircraft or spacecraftstructural components. In certain fields, such as automobile structuralcomponents, in addition to the structural and technical requirements ofthe cured composite article there is an added need for high throughput.Materials that are appropriate for aircraft or spacecraft may,therefore, not be adequate for use in automobiles—not because theresulting article is structurally inadequate, but because the means formaking such resulting article are too costly or time consuming.

There has been considerable effort made to reduce the cure cycle time ofmaterials for use in such high-throughput applications. Cure cycles area balance of temperature and time, taking into account the reactivity ofthe resin and the amount of resin and fiber employed. For example, theexothermic curing reaction of epoxy resins makes it easy for the systemto overheat, risking significant damage to the material and mold—so thecuring of epoxy resins cannot take place at temperatures that are toohigh and as a result can often take significant time. Althoughfast-curing resin formulations are known in the art (see, e.g.,WO-2014/096435 and EP-1279688), they can exhibit inferior development ofglass transition temperature (Tg) in the curing process, particularlywhen cured using short cure cycles in a press-molding process. Aninferior Tg increases the likelihood that the molded part distorts uponremoval from the hot mold and also leads to issues in applications wherethe article is expected to work at elevated temperatures. However, evenin formulations having an acceptable Tg, issues with handling resinformulations increase when the chemistry of ingredients allow for rapidcure cycles.

Resin systems have been developed with handling characteristics thatprovide very low or zero tack, e.g., for completely automated processes.See, e.g., EP 2268720 However, material with handling characteristics,including tack, that are suitable for processes that occur at ambient orslightly elevated temperatures (such as cross-ply and repositionapplications) remains elusive.

SUMMARY OF THE INVENTION

Therefore, there remains a need for a resin system capable of rapidcuring at a particular temperature that has adequate handlingcharacteristics (including tack and flexibility) across normal toelevated laminating environments (as defined by temperatures between 20°C. and 60° C.). In particular, such a curable resin cannot be too rigidto manipulate at handling temperatures (e.g., from 20° C. to about 60°C.), e.g., during lay up of materials. At the same time, however, thesame curable resin should not be so tacky that it adheres excessively tothe tool (e.g., instead of adhering properly to the reinforcing fibers),potentially resulting in the transfer of residue when repositioningmaterial or, in the case of uni-directional pre-preg, shredding apart ofthe material when it is repositioned on the tool. As used herein,“shredding apart” refers to the phenomenon where part of a materialremains in contact with the tool surface whilst the rest of the materialleaves the tool surface, and can occur when pre-preg is removed from atool for repositioning. Such a resin system would also preferably enablethe cured material to be demolded at temperatures near or at the curingtemperature.

Therefore, according to a first aspect of the present invention, thereis provided a curable resin comprising at least one thermosetting resin,at least one curative and at least one thermoplastic additive in a ratiosuch that the curable resin exhibits:

-   -   (i) a glass transition temperature (Tg) from about 130° C. to        about 200° C. when cured;    -   (ii) a cure conversion of at least 95% when cured for a duration        of no more than 10 minutes at a temperature of no more than        10° C. above the Tg of the curable resin when cured;    -   (iii) a phase angle of between 50° and 87°, and preferably        between 70° and 85°, when heated from 20° C. to 60° C.; and    -   (iv) optionally, a complex modulus of between about 100 Pa·s and        about 10,000,000 Pa·s between 20 and 60° C.

According to a second aspect of the present invention, there is provideda pre-preg of fiber-reinforced curable composite material, wherein saidpre-preg comprises at least one layer of reinforcing fibers impregnatedwith a curable resin as defined in detail herein.

According to a third aspect of the present invention, there is provideda process for the production of a molded article from a plurality ofpre-pregs, the process comprising:

-   -   (a) disposing a pre-preg as defined in detail herein into or        onto a mold;    -   (b) optionally repeating step (a) at least once to dispose one        or more further pre-pregs into or onto said mold; and    -   (c) curing the plurality of pre-pregs, preferably by thermally        curing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plot of phase angle versus temperature obtained fromheating various embodiments of the invention as compared to materialsdisclosed in the art.

DETAILED DESCRIPTION

As discussed above, the progression of a resin through the curingprocess can result in issues with handling, especially in short curecycles. The present inventors have discovered curable resins that notonly exhibit excellent handling characteristics (i.e., at ambienttemperature have a suitable phase angle and complex modulus, such thatthe resin is not too rigid to manipulate during lay-up), but alsoconsistently maintain these excellent characteristics at higher handlingtemperatures up to about 60° C. (e.g., consistently maintain a phaseangle that is not so high that the resin is too viscous for properadherence to the reinforcing fibers). Such curable resins also exhibitsuperior glass transition temperature (Tg) development in the curingprocess, particularly when cured using short cure cycles in apress-molding process.

The phase angle, the complex modulus G*, the storage modulus G′, and theloss modulus G″ provide assessments of the handling characteristics ofthe resin. The phase angle describes the physical state of the resin,where solid or semi-solid has a low phase angle and a more liquid orfluid material has a high phase angle. Thus, as a resin is heated, itsability to flow increases (corresponding to an increase in phase angle)until the action of the curative causes the resin to harden(corresponding to a decrease in phase angle). The complex modulus is theratio of stress to strain under vibratory conditions, and contains thestorage and loss components (i.e., the storage modulus G′ and the lossmodulus G″). These characteristics allow for an assessment of theelastic response and the viscous behavior of the resin material.

Thermosetting Resin

The curable resin comprises one or more thermosetting resin(s). Althoughthe formulation of the curable resin can be specified to achieve theoptimum performance for the intended use of the pre-pregs, thermosettingresins suitable for use in the present invention are preferably selectedfrom epoxy resins, resins comprising vinyl groups, and mixtures thereof.

In one embodiment, the thermosetting resin comprises, or even consists(essentially) of epoxy resins. Epoxy resins can be solid, liquid orsemi-solid and are characterized by their functionality and epoxyequivalent weight. The functionality of an epoxy resin is the number ofreactive epoxy sites per molecule that are available to react and cureto form the cured structure. The concentration of reactive groups in anepoxy resin is indicated by its epoxy equivalent weight, or EEW. The EEWis the weight (in Daltons) of epoxy resin material per reactive group.

Generally speaking, epoxy resins may be monofunctional, difunctional, ormultifunctional—where the term “multifunctional” refers to a resinhaving a functionality of greater than two. However, in the context ofthe present invention, the curable resin typically comprises one or moredifunctional or multifunctional epoxy resin(s). It is also noted thatthe term “multifunctional” also encompasses resins which havenon-integer functionality. The epoxy resin may further comprisemonofunctional epoxy resins or more than one type of difunctional and/ormultifunctional epoxy resins. In certain embodiments, the curable resincomprises one or more multifunctional epoxy resin(s) in combination withone or more difunctional epoxy resin(s).

Epoxy resins can, for example, be derived from the mono or poly-glycidylderivative of one or more of the group of compounds consisting ofaromatic diamines, aromatic monoprimary amines, aminophenols, polyhydricphenols, polyhydric alcohols, polycarboxylic acids and the like, or amixture thereof. Suitable epoxy resins include those based on:diglycidyl ether of bisphenol F, bisphenol A (optionally brominated),phenol and cresol epoxy novolacs or other glycidyl ethers ofphenol-aldehyde adducts, glycidyl ethers of aliphatic diols, diglycidylether, diethylene glycol diglycidyl ether, aromatic epoxy resins,aliphatic polyglycidyl ethers, epoxidised olefins, brominated resins,aromatic glycidyl amines, heterocyclic glycidyl imidines and amides,glycidyl ethers, fluorinated epoxy resins, aliphatic triglycidyl ethers,dialiphatic triglycidyl ethers, triglycidyl aminophenols, epoxy-modifiedpolyoxalidones or polyisocyanates, or any combinations thereof. Certainof the epoxy resins described above can exist in difunctional ormultifunctional form, as known to a person of skill in the art.

Epoxy resins suitable for use in the present invention may becommercially available, for example N,N,N′,N′-tetraglycidyl diaminodiphenylmethane (TGDDM) (e.g. grades MY 9663, MY 720, MY 721 or MY9512;Huntsman);N,N,N′,N′-tetraglycidyl-bis(4-aminophenyl)-1,4-diiso-propylbenzene (e.g.EPON 1071; Hexion);N,N,N′,N′-tetraglycidyl-bis(4-amino-3,5-dimethylphenyl)-1,4-diisopropylbenzene,(e.g. EPON 1072; Hexion); N,N,N′,N′-tetraglycidyl-m-xylenediamine;diglycidyl dihydroxy naphthalene; triglycidyl ethers of p-aminophenol(e.g. MY 0510; Hunstman); diglycidyl ethers of bisphenol A (DGEBA) basedmaterials such as 2,2-bis(4,4′-dihydroxy phenyl) propane (e.g. DER 661(Dow), or Epikote 828 (Hexion)) and higher molecular weight diglycidylethers of bisphenol A based materials such as those with an epoxyequivalent weight of 400-3500 g/mol (e.g. Epikote 1001 and Epikote1009); glycidyl ethers of phenol novolak (or novolac) resins (e.g. DEN431 or DEN 438; Dow); diglycidyl 1,2-phthalate (e.g. GLY CEL A-100);diglycidyl derivative of dihydroxy diphenyl methane (bisphenol F) (e.g.PY 306; Hunstman). Other epoxy resin precursors include cycloaliphaticssuch as 3′,4′-epoxycyclohexyl-3,4-epoxycyclohexane carboxylate (e.g. CY179; Hunstman).

In certain embodiments, the thermosetting resin is selected from resinswhich comprise an epoxy phenol novolac (EPN) resin in combination with adifunctional epoxy resin. In one embodiment, the difunctional epoxyresin is a bisphenol A epoxy resin, preferably diglycidyl ether ofbisphenol A (DGEBA).

In some embodiments, the thermosetting resin exhibits an EEW (epoxyequivalent weight) of at least about 90 g/mol, for example at leastabout 100 g/mol, and typically no more than about 400 g/mol, for exampleno more than about 300 g/mol. In certain embodiments, the curable resinexhibits an EEW (epoxy equivalent weight) of at least about 150 g/moland at most 250 g/mol.

In one embodiment, the thermosetting resin comprises, or even consists(essentially) of resins comprising vinyl groups, such as vinyl esterresins or urethane acrylate resins. Such resins may, in some cases, bereferred to as “vinyl hybrid resins.” Vinyl ester resins are typicallythe reaction products of epoxy resins and monofunctional ethylenicallyunsaturated carboxylic acids or anhydrides. Exemplary epoxy resins forinclusion in a vinyl ester resin include, but are not limited to,diglycidyl ether of bisphenol A and higher homologues thereof, thediglycidyl ether of tetrabromobisphenol A, epoxylated phenolformaldehydenovolac, and polypropylene oxide diepoxide—for example epoxylatedbisphenol A-epichlorohydrin and epoxylated phenolformaldehyde novolac.The carboxylic acid or anhydride can be any organic carboxylic acid oranhydride. Examples include acrylic acid, methacrylic acid, maleic acidor anhydride, succinic anhydride, fumaric acid, phthalic acid oranhydride, isophthalic acid, terephthalic acid, adipic acid, polyadipicanhydride, fatty acids, and mixtures of two or more thereof. Theacid-epoxide reaction can be catalyzed by tertiary amines, phosphines,alkalis, or onium salts.

Examples of commercially available vinyl ester resins include Derakane™780, a product of Dow identified as a solution of an acid functionalizednovolac vinyl ester resin dissolved in styrene monomer, Derakane™470-36, a product of Dow identified as an epoxy novolac vinyl esterresin dissolved in styrene monomer, and Derakane™ 411-45, a product ofDow identified as a solution of an epoxy vinyl ester resin dissolved inmonomeric styrene. Additional vinyl ester resins include the Advalite™family of resins, products of Reichhold identified as vinyl hybridresins that are either (monomer free) hot melt resins or (styrene free)liquid resins.

Curatives

As used herein, the term “curative” refers to a compound that effects,or assists in, the hardening of the curable resin, and hence the term“curative” generally includes catalysts, accelerators and hardeners(including stoichiometric hardeners). In some preferred embodiments, thecurable resin comprises one or more curatives selected from imidazolecuratives, (poly)amine and substituted (poly)amine curatives, peroxidecuratives and mixtures thereof. The type of curative is typically chosenbased on the type of thermosetting resin utilized. For example,imidazole curatives, (poly)amine and substituted (poly)amine curatives,are typically used with epoxy resins and peroxide curatives aretypically used with vinyl-containing resins.

Exemplary imidazole curatives include substituted imidazoles, preferablywherein the substituent groups of said substituted imidazoles are orcomprise alkyl and/or aryl substituent groups. Suitable substitutedimidazoles include6-(2-(2-methyl-1H-imidazol-1-yl)ethyl)-1,3,5-triazine-2,4-diamine,1-((2-methyl-1H-imidazol-1-yl)methyl)naphthalen-2-ol,3-(2-phenyl-1H-imidazol-1-yl)propanenitrile,(2-phenyl-1H-imidazole-4,5-diyl)dimethanol,bis(2-ethyl-5-methyl-1H-imidazol-4-yl)methane,6-[2-(2-ethyl-4-methylimidazol-1-yl)ethyl]-1,3,5-triazine-2,4-diamine,1H-imidazole, 2-methyl-1H-imidazole, 2-undecyl-1H-imidazole,1,2-dimethylimidazole, 2-ethyl-4-methylimidazole,2-undecyl-4-methylimidazole, 1-benzyl-2-methylimidazole,1-benzyl-2-phenylimidazole, 2-Phenylimidazole,2-phenyl-4-methylimidazole, 2-heptadecyl-1H-imidazole,6-(2-(2-methyl-1H-imidazol-1-yl)ethyl)-1,3,5-triazine-2,4-diamine,2-phenyl-4,5-dihydroxymethylimidazole,2-phenyl-4-methyl-5-hydroxymethylimidazole,2-phenyl-4-hydroxymethyl-5-methylimidazole,1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole,1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-phenylimidazole,1-cyanoethyl-2-undecylimidazolium trimellitate,1-cyanoethyl-2-phenylimidazolium trimellitate,2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine,2,4-diamino-6-[2′-undecylimidazolyl-(1′)]-ethyl-s-triazine,2,4-diamino-6-[2′-ethyl-4′-methylimidazolyl-(1′)]-ethyl-s-triazine,2,4-diamino-6-[2′-methylimidazolyl-(1′)]-ethyl-s-triazine isocyanuricacid adduct dihydrate, 2-Phenylimidazole isocyanuric acid adduct,2,3-dihydro-1H-pyrrolo[1,2-a]benzimidazole,1-dodecyl-2-methyl-3-benzylimidazolium chloride, 2-phenylimidazoline,2,4-Diamino-6-vinyl-1,3,5-triazine, 2,4-Diamino-6-vinyl-1,3,5-triazineisocyanuric acid adduct,2,4-Diamino-6-methacryloyloxyethyl-1,3,5-triazine,N1,N6-bis[2-(2-methyl-1H-imidazol-1-yl)ethyl]-hexanediamide,N,N′-Bis(2-methylimidazolyl-1-ethyl)urea, and mixtures thereof.

Exemplary (poly)amine and substituted (poly)amine curatives suitablyhave molecular weights of up to about 200 per amino group, and mayinclude aromatic amines, guanidine derivatives, and urone or ureaderivatives. Suitable diamines include, for example, 1,3-diaminobenzene,4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl sulphone (4,4′ DDS),3,3′-diaminodiphenyl sulphone (3,3′ DDS),bis(4-amino-3,5-dimethylphenyl)-1,4-diisopropylbenzene,bis(4-aminophenyl)-1,4-diisopropylbenzene,4-chlorophenyl-N,N-dimethyl-urea, 3,4-dichlorophenyl-N,N-dimethyl-urea,2,6- and 2,4-toluene bis dimethyl urea, dicyandiamide,4,4′-methylene-bis(phenyldimethylurea), cyanamide, methylene diphenyldiisocyanate (MDI) based ureas and mixtures thereof. In someembodiments, the curative used in connection with the present inventionis a combination of a substituted imidazole curative and a diaminecurative.

Exemplary peroxide curatives include organic acyl peroxides, peroxycarbonates, peroxyesters, peroxyketals, and (alkyl)peroxides. Suitableperoxides include, for example, dibenzoyl peroxide, di-t amyl peroxide,di-t butyl peroxide, dicumyl peroxide, t-butyl peroxy-2-ethylhexylcarbonate, t-amyl peroxy-2-ethylhexyl carbonate, di-(4-t-butylcyclohexyl)-peroxydicarbonate, t-butyl peroxybenzoate, t-butylperoxyacetate, t-butyl peroxy-2-ethylhexanoate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butyl monoperoxymaleate, t-amylperoxybenzoate, ethyl-3,3-di(t-butylperoxy) butyrate,1,1-di-(t-butylperoxy) cyclohexane,1,1-di-(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di-(t-amylperoxy)cyclohexane, 2,5-dimethyl-2,5-di-(2-ethylhexanoylperoxy)hexane,tert-butylperoxy isopropyl carbonate, 2,2-bis(tert-butylperoxy)butane,tert-butyl peracetate and mixtures thereof.

In some embodiments, the curatives used in connection with the presentinvention are solid curatives. Solid curatives are curatives whichremains solid until at least about 150° C., e.g., at least about 170°C., or even at least about 190° C., under atmospheric pressure. Thesolid curatives are used in the solid state and remain in the form of asolid during and after combining with any other ingredients that formthe curable resin, prior to curing. When in solid form, such curativesare suitably present in particulate or powder form. In some embodiments,the curatives of the present invention comprise a mixture of a solidcurative and a liquid curative. Liquid curatives are used in the liquidstate and remain in the form of a liquid during and after combining withany other ingredients that form the curable resin, prior to curing. Instill other embodiments, the curatives used in connection with thepresent invention are liquid curatives.

The curable resin generally comprises said curative(s) in an amount offrom about 1 wt % to about 15 wt %, for example from about 1.5 wt % or2.0 wt % to about 10 wt % or even from about 3 wt % to about 7 wt %based on the total weight of the curable resin.

Thermoplastic Additives

The curable resin comprises one or more thermoplastic additives. Withoutwishing to be bound by any particular theory, it is believed that thethermoplastic additive significantly enhances the ability to handle thecurable resin, while minimally impacting the cure conversion profile andglass transition temperature. Thermoplastic additives includepolyarylethersulfones, polysulfones, polyvinylformals such as vinylec Eor vinylec K, polymethylmethacrylates,polybutylacrylate-co-methylmethacrylate copolymers, polyimides,polyetherimides, phenoxy resins, modified butadiene nitrile polymers andpolyamides. In one embodiment, the curable resin comprises apolyarylethersulfone. In another embodiment, the curable resin comprisesa polyvinylformal resin. In still another embodiment, the curable resincomprises a phenoxy resin. In still another embodiment, the curableresin comprises a polyamide resin.

Generally speaking, the curable resin comprises one or morethermoplastic additives in an amount of from about 2 wt % to about 10 wt%. For example, in some embodiments, the curable resin comprises fromabout 2 wt % to about 8 wt %, or even from about 4 wt % to about 7 wt %.For the sake of clarity, the weight percentages of thermoplasticadditives refer to the total amount of thermoplastic additive (i.e., incombination, if such combination is present).

Additional Additives

The curable resin may further contain conventional additives. In someembodiments, the curable resin comprises additional toughening agents,fillers or stabilizers. Suitable toughening agents include, for example,particulate toughening agents and aggregates such as glass beads, rubberparticles and rubber-coated glass beads. Suitable fillers include, forexample, polytetrafluoroethylene, silica, graphite, boron nitride, mica,talc and vermiculite, pigments, nucleating agents, clays, flameretardants such as alumina trihydrate (ATH) and magnesium hydroxide(MDH). Suitable stabilisers include phosphates. Additives may furtherinclude core-shell rubbers, such as core-shell rubbers in Kaneka's ACEMX product range, and liquid rubbers having reactive groups. The totalamount of said additives in the curable resin is such that saidadditives constitute typically no more than about 10 wt %, moretypically no more than about 5 wt %, by total weight of the pre-preg.

In some embodiments, the curable resin does not contain a cureinhibitor. For example, in some embodiments, the curable resin does notcontain a cure inhibitor which is or comprises boric acid (includingderivatives thereof such as metaboric acid and boric anhydride), a Lewisacid derivative of boron such as an alkyl borate or an alkyl borane ortrimethoxyboroxine, a mineral acid having a nucleophilicity value “n”(as measured in C. G. Swain and C. B. Scott in J. Am, Chem. Society,Vol. 75, p 141 (1953)) of greater than zero and less than 2.5 (forexample perchloric acid or tetrafluoroboric acid, fluoroarsenic acid,fluoroantimonic acid, fluorophosphoric acid, chloroboric acid,chloroarsenic acid, chloroantimonic acid chlorophosphoric acid, chloricacid, bromic acid, iodic acid and any combination thereof), or anorganic acid having a pKa value of from 1 to 3 (such as salicylic acid,oxalic acid and maleic acid and mixtures thereof).

Properties of the Curable Resin

The glass transition temperature (Tg) of the curable resin, when cured,is in the range of from about 130° C. to about 200° C. In someembodiments, the glass transition temperature (Tg) of the curable resin,when cured, is from about 150° C. to about 200° C., or even from about160° C. to about 180° C. In some embodiments, the curable resins havecure temperatures that are no more than 20° C. greater than, e.g., nomore than 10° C. greater than, the Tg of the curable resin, when cured.In some embodiments, the curable resins have cure temperatures that areno more than, and preferably less than, the Tg of the curable resin,when cured. It will be appreciated that these Tg values refer to thecured resin when in a state of cure defined by a cure conversion of atleast 95%.

The curable resin of the present invention exhibits a cure conversion(measured as described herein) of at least 95% when cured for a durationof no more than 10 minutes (e.g., in some embodiments no more than 8 oreven no more than 5 minutes) at a temperature of no more than 10° C.above the Tg of the curable resin when cured. Generally, “95% cureconversion” defines a material where a sufficient majority of thereactive sites have been consumed, such that the mechanical and thermalcharacteristics of the cured material are within suitable characteristicranges for that material. While it is possible to obtain additionalcuring with additional time, this will typically not result insignificant mechanical or thermal improvement. In some embodiments, thecurable resin of the present invention exhibits a cure conversion of atleast 95% (e.g., in some embodiments at least 98%) when cured at a curetemperature in the range of from about 120° C. to about 175° C., whereinthe cure cycle has a duration of no more than 10 minutes (e.g., in someembodiments no more than 8 minutes or even no more than 5 minutes).

In many conventional prior art resin systems where relatively high moldtemperatures are used to obtain rapid cure times, the cure temperatureis significantly higher (for instance at least 20° C. or at least 10° C.more) than the Tg of the cured resin. While the resin component is fullycured under these conditions, it is too soft to be removed from the mold(for instance without posing a high risk of distortion), and it isnecessary to cool the mold to below the Tg of the cured resin beforeremoving the cured component from the mold. Such a cooling step is anadditional, undesirable step which increases the time required toproduce a component, lowers the number of components that can beproduced by a mold during a work cycle, and undesirably increases costs.Accordingly, in some embodiments, the curable resin of the presentinvention exhibits a cure conversion (measured as described herein) ofat least 95% when cured for a duration of no more than 10 minutes (e.g.,in some embodiments no more than 8 or even no more than 5 minutes) at atemperature less than the Tg of the curable resin when cured. In suchembodiments, it would be possible to demold the cured resin when themold is still hot—thus decreasing the time and costs associated withproducing the cured component.

In some embodiments, the curable resin exhibits an uncured glasstransition temperature (Tg) of less than 8° C. In further embodiments,the curable resin exhibits an uncured glass transition temperature (Tg)of less than 6° C., or even less than 3° C. In still furtherembodiments, the curable resin exhibits an uncured glass transitiontemperature (Tg) of at least about −6° C.

In some embodiments, the curable resin exhibits a viscosity at 21° C. ofless than 1,500,000 Pa·s. It is noted, however, that measuring viscosityat a single temperature and shear rate only provides a small portion ofthe full picture related to the rigidity and integrity of a material.Instead, a variety of oscillatory shear testing can more adequatelydefine the material by measuring the complex modulus (G*), the elastic(or storage) modulus (G′), the viscous (or loss) modulus (G″), and thePhase angle (δ). In particular, the phase angle and complex modulustogether can define a viscoelastic map (as shown below and reproducedfrom http://www.rheologyschool.com), which, from left to right,distinguishes between elastic solids and viscous liquids and, from topto bottom distinguished between high and low rigidity or viscosity.

Accordingly, in some embodiments, the curable resins of the presentinvention exhibit a complex modulus (G*) of between about 100 and about10,000,000 Pa·s between 20° C. and 60° C. For example, in someembodiments, the curable resins of the present invention exhibit acomplex modulus (G*) of between about 1,000 Pa·s and about 5,000,000Pa·s, or between about 4,000 Pa·s and about 4,000,000 Pa·s. The complexmodulus is essentially a measure of how difficult it is to deform amaterial, e.g., a measure of flex/drapeability. A workable range for thecomplex modulus (G*) is defined by a pre-preg that is not too flaccid tobe handled, nor too rigid to be useful.

The curable resins of the present invention exhibit a phase angle ofbetween 50° and 87°, and preferably between 70° and 85°, when heatedfrom 20° C. to 60° C. As used herein, the language “exhibit(s) a phaseangle between A and B when heated from X to Y” means that the phaseangle remains between A and B for the temperature range between X and Y.In some embodiments, the curable resins of the present invention exhibita phase angle of between 72° and 84° when heated from 20° C. to 60° C.In some embodiments, the phase angle exhibited by the curable resins ofthe present invention peaks at between 72° and 84° when heated from 20°C. to 60° C., followed by a decrease in phase angle within the same 20°C. to 60° C. range. In some embodiments, the phase angle exhibited bythe curable resins of the present invention peaks at between 72° and 84°when heated from 20° C. to 60° C., followed by a decrease in phase angleof at least about 2° within the same 20° C. to 60° C. range. In someembodiments, the phase angle exhibited by the curable resins of thepresent invention peaks at between 76° and 84° when heated from 20° C.to 60° C., followed by a decrease in phase angle of at least about 4°within the same 20° C. to 60° C. range. In sum, the curable resins ofthe present invention unexpectedly exhibit excellent handlingcharacteristics at normal and elevated laminating temperatures.

In some embodiments, the curable resins of the present invention exhibita phase separation during the temperature range. Without wishing to bebound by theory, it is believed that the thermoplastic additivedissolves in the base resin (which reduces the phase angle), but tendsto partially phase separate upon cooling. This phase separation mayallow for a flatter phase angle trace over temperature, instead ofsimply increasing with increased temperature (as in conventional resinformulations).

In some embodiments, the curable resins of the present invention exhibitan elastic (or storage) modulus (G′) of between about 500 Pa and about6,000,000 Pa at 20° C., e.g., between about 1,000 Pa and about 4,000,000Pa at 20° C. or even between about 2,000 Pa and about 2,000,000 Pa at20° C. In some embodiments, the curable resins of the present inventionexhibit an elastic (or storage) modulus (G′) of between about 10 Pa andabout 2,500 Pa at 60° C., e.g., between about 25 Pa and about 1,000 Paat 60° C. The Dahlquist criterion, which is derived from the conclusionthat tack is a modulus-controlled process, specifies that tack does notoccur when the adhesive storage modulus is greater than 10⁵ Pa. However,in some embodiments, the curable resins of the present invention exhibittack even with a storage modulus of greater than 10⁵ Pa.

In some embodiments, the curable resins of the present invention exhibita viscous (or loss) modulus (G″) of between about 6 Pa and about10,000,000 Pa at 20° C., e.g., between about 8 Pa and about 8,000,000 Paat 20° C. In some embodiments, the curable resins of the presentinvention exhibit a viscous (or loss) modulus (G″) of between about 100Pa and about 5,000 Pa at 60° C., e.g., between about 200 Pa and about1,800 Pa at 60° C.

Exemplary Curable Resin Formulations

While it is possible to derive other formulations exhibiting theproperties described herein, some embodiments include compositionscomprising:

about 70% to about 90% of a mixture of difunctional and/ormultifunctional thermosetting epoxy resins,

about 5% to about 10% of a curative selected from substitutedimidazoles, ureas, urones and mixtures thereof; and

about 3% to about 7% of a thermoplastic additive selected from phenoxyresins, polyvinylformal resins, polyethersulfone resins, and mixturesthereof.

Other embodiments include compositions comprising:

about 70% to about 99% of a vinyl ether resin or a mixture of vinylether resins,

about 1% to about 4% of a curative selected from organic acyl peroxides,peroxy carbonates, peroxyesters, peroxyketals, peroxides and mixturesthereof; and

about 3% to about 7% of a thermoplastic additive selected from phenoxyresins, polyvinylformal resins, polyethersulfone resins, and mixturesthereof.

All percentages listed above are weight percent versus the total weightof the curable resin. Exemplary formulations are described below inTables 1-5.

TABLE 1 Exemplary Formulation Ingredient % Bisphenol A diglycidyl ether(DGEBA) as solid,  25-35% liquid or a combination thereof Epoxy phenolnovolac  50-60% Phenoxy Resin 3%-7% Dicyandiamide (DICY) 3%-7%Substituted urea catalyst 2%-6%

TABLE 2 Exemplary Formulation Ingredient % Bisphenol A diglycidyl ether(DGEBA) as solid, 60%-70% liquid or a combination thereofTetrafunctional epoxy resin  15-25% Polyvinylformal resin 1%-3%Polyethersulfone 1%-3% Dicyandiamide (DICY) 3%-7% Solid disubstitutedimidazole curative, e.g., 1%-4%6-(2-(2-methyl-1H-imidazol-1-yl)ethyl)-1,3,5- triazine-2,4-diamineSubstituted urea catalyst 1%-4%

TABLE 3 Exemplary Formulation Ingredient % Epoxy phenol novolac 65%-75%Polyvinylformal resin 3%-7% Solid epoxy resin 4%-8% Dicyandiamide (DICY)3%-7% Bisphenol A diglycidyl ether (DGEBA) as solid,  5%-15% liquid or acombination thereof. Solid disubstituted imidazole curative, e.g., 1%-4%6-(2-(2-methyl-1H-imidazol-1-yl)ethyl)-1,3,5- triazine-2,4-diaminePigment 0.01%-1%  

TABLE 4 Exemplary Formulation Ingredient % Bisphenol A diglycidyl ether(DGEBA) as solid, 45%-60% liquid or a combination thereof. Additionalmultifunctional epoxy resin, e.g., 25-40% tetrafunctional epoxy resinPolyethersulfone 3%-7% Dicyandiamide (DICY) 3%-7% Solid disubstitutedimidazole curative, e.g., 2%-5% 1-(cyanoethyl)-2-ethyl-4-methylimidazole

TABLE 5 Exemplary Formulation Ingredient % Bisphenol A diglycidyl ether(DGEBA) as solid, 30%-50% liquid or a combination thereof. Additionalmultifunctional epoxy resin, e.g., 40%-60% tetrafunctional epoxy resinPolyvinylformal resin, e.g., vinylec K 2%-5% Dicyandiamide (DICY) 3%-7%Substituted urea catalyst 1.5%-3.5%

TABLE 6 Exemplary Formulation Ingredient % Vinyl hybrid hot melt resin60%-80% Vinyl hybrid liquid resin 15%-25% Polyvinylformal resin, e.g.,vinylec K 4%-7% Peroxyester 1.5%-2.2%

TABLE 7 Exemplary Formulation Ingredient % Vinyl hybrid hot melt resins(e.g., more than one, 54%-66% in combination) Vinyl hybrid liquid resin25%-35% Polybutylacrylate-co-methylmethacrylate copolymer 4.5%-7.5%Peroxyester 1.5%-2.2%

Pre-Pregs

The present invention also includes pre-pregs of fiber-reinforcedcurable composite materials. The pre-pregs of the present inventioncomprise or consist of one or more layer(s) of reinforcing fibersimpregnated with a curable resin as defined in detail herein.Preferably, the layer(s) of reinforcing fibers are impregnated with saidcurable resin. As used herein, the term “impregnated” means that thecurable resin is present throughout the cross-section of the pre-preg,i.e. the curable resin is present in interstices between the reinforcingfibers or bundles of reinforcing fibers throughout the cross-section ofthe pre-preg.

In the present disclosure, the proportions of the various components aresuch that the amount of reinforcing fibers plus the amount of curableresin equals 100%. It will be appreciated that reference to the “curableresin” in this context includes the curable resin components themselves,the curative(s) and the optional additives described hereinabove.

Pre-pregs of the present invention typically comprise from about 30 toabout 80% of curable resin, wherein the percentages refer to volumepercent of the curable resin, by total volume of the pre-preg. Forexample, the pre-preg may contain from about 30 to about 65%, or fromabout 45% to about 55%, of the curable resin. In some embodiments, thepre-preg comprises at least about 40% of the curable resin. In someembodiments, the pre-preg comprises no more than about 65%, or no morethan about 60%, of the curable resin. Where the reinforcing fibers areselected from carbon fiber, the pre-preg typically comprises from about30 to about 65 wt % of curable resin by total weight of the pre-preg,for example, from about 40 to about 55 wt % of curable resin by totalweight of the pre-preg. The narrower and narrowest ranges of resinfractions are particularly advantageous for achieving the desiredpermeability characteristics described herein.

In some embodiments, the pre-preg exhibits an areal weight of from about100 to about 1000 g/m², for example from about 100 to about 750 g/m²,from about 200 to about 500 g/m², or even from about 250 to about 650g/m². Areal weights within the recited ranges are particularlyappropriate for pre-pregs in which the reinforcing fibers are selectedfrom carbon fiber. It will be understood that the areal weight of thepre-preg includes the weight of the reinforcing fibers and the curableresin (i.e. including the curative(s) and any optional additivescontained therein).

In some embodiments, the thickness of the pre-preg is no more than about1500 μm, e.g., no more than about 1000 μm, or in some embodiments nomore than about 500 μm. In other embodiments, the thickness of thepre-preg is based on the number of plys in the material. For example, insome embodiments, the thickness of the pre-preg is between about 15 μm,and about 450 μm per ply.

Fibers

As used herein, the term “fiber” has its ordinary meaning as known tothose skilled in the art and may include one or more fibrous materialsadapted for the reinforcement of composites, which may take the form ofany of particles, flakes, whiskers, short fibers, continuous fibers,sheets, plies, and combinations thereof. In certain embodiments, thefibers are arranged as a fiber pre-form. As used herein, “fiberpre-form” refers to an assembly of fibers, layers of fibers, fabric orlayers of fabric plies configured to receive a liquid curable resin in aresin infusion process. In some embodiments, the fibers in a reinforcingfiber layer are in the form of continuous fibers, filaments, tows,bundles, sheets, plies, or combinations thereof. The precisespecification of the fibers, for instance their orientation and/ordensity, can be specified to achieve the optimum performance for theintended use of the pre-pregs. Continuous fibers may adopt any ofunidirectional (aligned in one direction), multi-directional (aligned indifferent directions), non-woven, woven, knitted, stitched, wound,twisted, untwisted and braided configurations. In certain preferredembodiments, the reinforcing fibers are in the form of untwisted bundlesof continuous filaments. Woven fiber structures may comprise a pluralityof woven tows, each tow composed of a plurality of filaments. In furtherembodiments, the tows may be held in position by cross-tow stitches,weft-insertion knitting stitches, or a small amount of resin binder,such as a thermoplastic resin. In one embodiment, the layer(s) ofreinforcing fibers used in the present invention comprise woven fiberstructures comprising a plurality of woven tows arranged substantiallyorthogonally. In a further embodiment, the layer(s) of reinforcingfibers used in the present invention comprise fiber structures whereinthe fibers are arranged unidirectionally. In a further embodiment, thelayer(s) of reinforcing fibers used in the present invention comprisefiber structures wherein the fibers are arranged in other orientations,such as tri-axial wherein fibers are arranged in three directions, suchas 0°, +60°, −60°.

The reinforcing fibers are selected from, but not limited to, glassfibers (including Electrical or E-glass), carbon fibers (particularlygraphite), aramid, synthetic polymer fibers (such as aromatic polyamidefibers, polyimide fibers, polybenzoxazole fibers, high-moduluspolyethylene (PE) fibers and polyester fibers), boron fibers, quartzfibers, basalt fibers, ceramic fibers (such as silicon carbide fibers),and combinations thereof. In one embodiment, the fibers comprise carbonfibers, glass fibers, or a combination thereof. Carbon fiber isparticularly suitable. In one embodiment, the fibers comprise carbonfibers that exhibit a tensile strength of greater than or equal to 3.5GigaPascals (“GPa”) and a tensile modulus of greater than or equal to200 GPa. For the fabrication of high-strength composite materials, e.g.for aerospace and automotive applications, it is preferred that thereinforcing fibers have a tensile strength of greater than 3.5 GPa.

Pre-pregs of the present invention typically comprise from about 20 toabout 70% reinforcing fibers, wherein the percentages refer to thevolume percent of the fiber by total volume of the pre-preg. Forexample, the pre-preg may contain from about 35 to about 70%, or fromabout 45% to about 60% reinforcing fibers. In some embodiments, thepre-preg comprises no more than about 60% reinforcing fibers. In someembodiments, the pre-preg comprises at least about 35%, at least about40%, or at least about 45% reinforcing fibers. Where the reinforcingfibers are selected from carbon fiber, the pre-preg typically comprisesfrom about 40 to about 80 wt % reinforcing fibers, by total weight ofthe pre-preg. For example, the pre-preg may contain from about 45 toabout 70 wt %, from about 55% to about 70 wt %, or from about 56 toabout 68 wt %, by total weight of the pre-preg. In some embodiments, thepre-preg comprises no more than 75 wt %, e.g., no more than about 70 wt%, reinforcing fibers by total weight of the pre-preg. The narrower andnarrowest ranges of reinforcing fiber fractions are particularlyadvantageous for achieving the desired permeability characteristicsdescribed herein.

Manufacturing

The pre-pregs of the present invention are manufactured by any suitabletechnique known in the art, such that the curable resin described hereinis contacted with the fibrous reinforcing agent in one or more of theforms noted above under conditions of temperature and pressuresufficient to cause the curable resin to flow and infuse or impregnatethe fibers. The term “impregnate” refers to the introduction of acurable resin to reinforcement fibers so as to introduce the curableresin between the interstices of the fibers and/or fully or partiallyencapsulate the fibers. Thus, the pre-preg of the present invention isprepared by the general method of:

-   -   providing a dry fiber pre-form comprised of one or more layers        of reinforcing fibers; and    -   impregnating said dry fiber preform with the curable resin,        wherein said curable resin is liquid.

In general terms, the dry fiber pre-form is impregnated with the curableresin by heating the curable resin to its molten state and disposingsaid molten curable resin on and into said dry fiber preform. Typicalimpregnating methods include:

-   -   (1) Continuously moving the reinforcing fibers through a bath of        solvated resin composition to fully or substantially fully wet        out the fibers; followed by the application of heat to evaporate        the solvent; or    -   (2) Pressing top and/or bottom resin films against a web of        reinforcing fibers under elevated temperature.        The resulting pre-preg is generally a pliable sheet of material,        which is typically tacky, but may also exhibit low or no tack.

In some embodiments, the pre-preg is prepared by a hot-melt castingtechnique. The hot-melt pre-preg manufacturing process is disclosed inWO-2014/096435-A, which is incorporated herein by reference.

To form a molded article, a plurality of pre-pregs is laid up into oronto a mold (often referred to as molding tool) in a stackingarrangement to form a “pre-preg lay-up”. The pre-preg plies within thelay-up may be positioned in a selected orientation with respect to oneanother. For example, pre-preg lay-ups may comprise pre-preg plieshaving uni-directional fiber arrangements, with the fibers oriented at aselected angle θ, e.g., 0°, 45°, or 90°, with respect to the largestdimension (typically defined as the length) of the lay-up. Once inplace, the pre-pregs in the lay-up are cured as described hereinbelow.

The layup process can be an automated process. Automated handling offiber-reinforced composite materials (including pre-pregs) is known,e.g., in US 2005/0042323 or U.S. Pat. No. 7,341,086, the disclosure ofwhich is incorporated herein by reference. However, in some embodiments,the layup process may be fully or partially manual. For example, thelayup process may be a hand layup process. In some embodiments, thelayup process may include cross-plying, repositioning, pad-ups orply-drops, preforming, laminating onto a tool, or any combinationthereof.

There is also provided herein, a process for the production of a moldedarticle from a plurality of pre-pregs, the process including:

-   -   (a) disposing a pre-preg into or onto a mold;    -   (b) repeating step (a) at least once to dispose one or more        further pre-pregs into or onto said mold; and    -   (c) curing the plurality of pre-pregs, e.g., by thermally        curing;        wherein said pre-preg comprises the curable resin and the        reinforcing fiber as each defined herein.

In some embodiments, this process is a press-molding process. In someembodiments, this process is an automated process. The process may alsobe an automated press-molding process.

The pre-preg can be provided in the form of a wound roll of the pre-pregmaterial (typically wound around a core of cardboard or other suitablematerial). The process of producing a molded article, therefore, mayfurther comprise the step of unwinding the pre-preg material onto a flatand level base and suitably securing the pre-preg material in positionby a suitable securing means as is conventional in the art. One or morepre-determined shapes can also be cut from the web of pre-preg material,optionally using a mechanized and automated cutting means, as known inthe art. One suitable cutting means is a high-frequency rotationallyoperating oscillating saw blade. During the cutting step, the web ofpre-preg may be supported and retained in place by a suitable retainingmember. The pre-determined cut shape remains in the plane of the web ofthe remaining pre-preg material. The pre-preg (or the pre-determined cutpre-preg shape) is then conveyed into or onto the mold. Optionally, thecut pre-preg shape may be conveyed to a stacking position where the cutpre-preg shapes are stacked or wherein the cut pre-preg shapes aredeposited in or on a release film or lay-up mold or mold loading device,and then conveyed into or onto said mold.

After the desired or pre-determined number of pre-pregs has been laid inor on the mold, the plurality of pre-pregs are cured. Although thermalcuring is preferred, UV or light curing is also contemplated. In someembodiments, curing is effected while the pre-pregs are located in or onthe mold, for example while the pre-pregs are compressed in a moldcavity, preferably a heated mold-cavity. In some embodiments, the heatedmold-cavity is an isothermally heated mold cavity. Thus, curing can beeffected in a press-molding process where the temperature of the moldingsurfaces of the mold is fixed at a pre-determined temperature(isothermal tooling) to cure the pre-pregs. Thus, when the pre-pregs arecompressed by a mold (e.g., a mold tool or mold press), at least aportion of the pre-pregs is in contact with the desired and appropriatemolding surface(s) of the mold. The pre-pregs are therefore heated asquickly as the mold allows. In other embodiments, the heated mold rampsup in temperature: beginning at ambient or slightly above ambient andincreasing to a temperature suitable to cure the pre-preg. The moldtemperature may optionally then be ramped down prior to or after thede-molding of the cured part.

In the present invention, thermal curing is generally conducted at acure temperature (Tc) of at least 120° C., e.g., at least 140° C. Insome embodiments, thermal curing is generally conducted at a curetemperature (Tc) of no more than 175° C., e.g., no more than 165° C. Insome embodiments, thermal curing is generally conducted at a curetemperature (Tc) in the range of from about 120° C. to about 175° C.,for example from about 140° C. to about 165° C. In certain embodiments,thermal curing is conducted at a cure temperature (Tc) which is no morethan 20° C. greater than, e.g., no more than 10° C. greater than the Tgof the curable resin when cured. In certain embodiments, thermal curingis conducted at a cure temperature (Tc) which is no more than, and ispreferably less than, the Tg of the curable resin when cured. In otherwords, in some cases Tc≤Tg+20° C., in some cases Tc≤Tg+10° C., and insome cases Tc≤Tg and more preferably Tc<Tg. In some embodiments, thermalcuring is conducted using a cure cycle having a duration of no more than10 minutes, e.g., no more than 8 minutes, or even no more than 5minutes. The cure cycle duration as defined herein is the period forwhich the plurality of pre-pregs is subjected to the pre-determined curetemperature and does not include the ramp phase or the cool-down phase.

In an alternative embodiment, thermal curing may be conducted in an ovenor autoclave, and may be conducted under vacuum (for instance in avacuum bag as known in the art), suitably conducted at elevatedpressure. Suitable elevated pressures include pressures from about 2 toabout 10 bar. In this embodiment, the cure temperatures and cure cycledurations described hereinabove are also applicable, but typically theheating and cooling rates are controlled. Typically, the heating rateduring the ramp phase is from about 1 to about 5° C./min, more typicallyfrom about 1 to about 3° C./min. Typically, the cooling rate in thecool-down phase is from about 1 to about 5° C./min, more typically fromabout 1 to about 3° C./min to 60° C.

The process further comprises the step of removing the molded curedpre-preg(s) from the mold to provide the molded article. The curableresins of the present invention are particularly advantageous becausethey allow the molding process to dispense with the step of cooling themold before removing the cured component therefrom. Indeed, in someembodiments of the present process, such process does not comprise thestep of cooling the mold prior to removing the molded cured pre-preg(s)therefrom.

Molded articles prepared by the process described herein areparticularly suitable as components for transport applications, andparticularly the automotive industry. The term “automotive industry”herein is a particular reference to road transport vehicles, includingcars, buses, trucks and motorcycles and the like. Automotive componentsprepared by the present invention are particularly suitable as mid- orhigh-volume automotive parts, particularly those where cost and speed ofproduction are paramount. For example, components prepared by thepresent invention can include structural parts such as body or chassiscomponents, e.g. spare wheel wells, body panels, boot lids, etc.Components prepared by the present invention can also include visualquality parts, such as hoods, roofs, rockers, splitters, spoilers, amongothers. The present invention provides a process which providesadvantages of efficiency and economy. The lay-up time according to thepresent invention is significantly reduced, allowing a reduction in theunit cost per component and/or allowing the high volume of componentproduction desired in the automotive industry. Moreover, the enhancedand consistent manipulability of the curable resin can allow for aneasier, and potentially quicker, lay-up process.

Various embodiments of the invention are described herein. It will berecognized that features specified in each embodiment may be combinedwith other specified features to provide further embodiments.

Exemplification

The present teachings are further illustrated with reference to thefollowing non-limiting examples.

Exemplary Materials

Exemplary commercially available material used in the following examplesincludes:

Ingredient Commercially available source Epoxy phenol novolac Epikote ®154 Epoxy phenol novolac Araldite ® EPN1138 Tetrafunctional epoxy resinAraldite ® MY 9512 Phenoxy resin YD50 Polyvinyl formal resin Vinylec Eor Vinylec K Dicyandiamide (DICY) Dyhard ® 100SF Dicyandiamide (DICY)Dyhard ® DF50EP (50% dispersed in a 50% Bisphenol-A epoxy resin)Bisphenol A diglycidyl ether Araldite ® LY1556 (liquid) (DGEBA)Bisphenol A diglycidyl ether Araldite ® GT7071 (solid) (DGEBA)Substituted urea catalyst Dyhard ® UR505 Substituted urea catalystOmicure ® U-24 6-(2-(2-methyl-1H-imidazol- Curesol ® 2MZ Azine S1-yl)ethyl)-1,3,5-triazine- 2,4-diamine 1-(cyanoethyl)-2-ethyl-4-Curimid ® CN methylimidazole Pigment WS17321A Vinyl hybrid hot meltresin Advalite ™ 35000-00 Vinyl hybrid hot melt resin Advalite ™35051-00 Vinyl hybrid hot melt resin Advalite ™ X4710-16 Vinyl hybridliquid resin Advalite ™ 35060-00 Vinyl hybrid liquid resin Advalite ™35065-00 Polybutylacrylate-co- Nanostrength ™ M22N methylmethacrylatecopolymer Peroxyester Luperox ® 270 Peroxyester Trigonox ® 21S

Measurement Methods

The pre-pregs described herein were characterized as follows.

Viscosity

The viscosity of the resins was measured as a temperature sweep using athermo HAAKE MARS rheometer in oscillation mode unless otherwise stated,by following ASTM D4440-15: using an 8 mm diameter parallel plate, witha strain of 1%, a frequency of 1 Hz and a gap of 500 μm. Values forcomplex modulus (G*), elastic (or storage) modulus (G′), viscous (orloss) modulus (G″), and phase angle (δ) are derived from the viscositydata measured according to this method.

Glass Transition Temperature

The glass transition temperature, T_(g), of the cured resins wasmeasured by Dynamic Mechanical Analysis (DMA) using a dynamic mechanicalanalyser (TA Instruments Q800) under flexural oscillation mode accordingto ASTM 7028-07, with a heating rate of 5° C./min and without purge gas.The thermocouple in the TA Instruments Q800 equipment remained in itsfixed position. The dimensions of the sample were 58±5×10±1×1.75±0.75 mm(Length×Width×Thickness). The Tg reported herein is the intercept of thetwo tangent lines (i.e. the Lines “A” and “B” referred to in ASTM7028-07) from the plot of storage modulus on a linear scale vs.temperature.

The uncured glass transition temperature, T_(g), of the resins wasmeasured by differential scanning calorimetry (DSC) at a heating rate of10° C. per minute, according to ISO 11357-2:2013, on a TA InstrumentsQ2000 differential scanning calorimeter.

Cure Conversion

Differential Scanning calorimetry (DSC) was utilized to determine thecure conversion under a given set of cure conditions, substantially inaccordance with ISO-11357-5:2013. The residual enthalpy (remaining heatof reaction) detected during the DSC measurement is correlated to thetotal enthalpy (heat evolved) of the curing reaction. DSC measurementsare performed by heating a sample from 30° C. to a temperature that issufficient to capture the entire curing reaction (225° C. is typicallysufficient for the resins described herein) at a heating rate of 10°C./min. The sample size is about 5-10 mg. The cure conversion (%) iscalculated as:

${{cure}\mspace{14mu} {coversion}\mspace{14mu} (\%)} = {\frac{\left( {{\Delta \; {Hi}} - {\Delta \; {He}}} \right)}{\Delta \; {Hi}} \times 100}$

wherein:ΔHi is the enthalpy generated by the uncured test sample during heatingfrom 30° C. to 225° C.; andΔHe is the enthalpy generated by a cured sample during the heating scanof heated from 30° C. to 225° C.

Example 1

An epoxy resin formulation according to Table 8 below was prepared bymixing the first three ingredients at 170° C. for two hours under lowshear. The mixture was cooled to 50° C., followed by the addition of theremainder of the materials. The resulting mixture was mixed for 10minutes.

TABLE 8 Epoxy resin formulation of Example 1 Ingredient % bisphenol Adiglycidyl ether (DGEBA) 29.48 epoxy phenol novolac 56.52 phenoxy resin5.00 dicyandiamide (DICY) 5.00 substituted urea catalyst 4.00

A pre-preg was prepared from the epoxy resin formulation of Example 1 asfollows: A carbon fibre fabric (2×2 twill weave; areal weight of 200gsm) manufactured from a 3 k fibre (e.g., SM T300 3K from Toray®) wasimpregnated with the epoxy resin formulation of Example 1 to obtain aprepreg with a resin content of 38%. The pre-preg was used to make an8-ply 0/90° laminate which was then subjected to a 5 minute cure at acuring temperature of 160° C. The curing was performed in asteel-matched die tool pre-heated to the curing temperature. Theresulting laminate was tested by DMA following ASTM 7028-07, and foundto exhibit a Tg of about 150° C.

The viscosity of the resin formulation of Example 1 was analyzed asdescribed above. The formulation according to Example 1 exhibits a phaseangle of between 70° and 87° when heated from 20° C. to 60° C.Additional shear properties of the resin formulation of Example 1 areprovided in Table 15, below.

Example 2

An epoxy resin formulation according to Table 9 below was prepared bymixing the first four ingredients at 170° C. for three hours under lowshear. The mixture was cooled to 50° C., followed by the addition of theremainder of ingredients. The resulting mixture was mixed for 10minutes.

TABLE 9 Epoxy resin formulation of Example 2 Ingredient % bisphenol Adiglycidyl ether (DGEBA) 66.12 tetrafunctional epoxy resin 21.08polyvinyl formal resin 1.70 polyethersulfone 1.70 dicyandiamide (DICY)4.40 6-(2-(2-methyl-1H-imidazol-1-yl)ethyl)- 2.501,3,5-triazine-2,4-diamine substituted urea catalyst 2.50

A pre-preg was prepared from the epoxy resin formulation of Example 2 asfollows: A carbon fibre fabric (2×2 twill weave; areal weight of 200gsm) manufactured from a 3 k fibre (e.g., SM T300 3K from Toray®) wasimpregnated with the epoxy resin formulation of Example 2 to obtain aprepreg with a resin content of 38%. The pre-preg was used to make an8-ply 0/90° laminate which was then subjected to a 5 minute cure at acuring temperature of 160° C. The curing was performed in asteel-matched die tool pre-heated to the curing temperature. Theresulting laminate was tested by DMA following ASTM 7028-07, and foundto exhibit a Tg of about 152° C.

The viscosity of the resin formulation of Example 2 was analyzed asdescribed above. The formulation according to Example 2 exhibits a phaseangle of between 70° and 87° when heated from 20° C. to 60° C.Additional shear properties of the resin formulation of Example 2 areprovided in Table 15, below.

Example 3

An epoxy resin formulation according to Table 10 below was prepared bymixing the first four ingredients at 170° C. for two hours under lowshear. The mixture was cooled to 50° C., followed by the addition of theremainder of ingredients. The resulting mixture was mixed for 10minutes.

TABLE 10 Epoxy resin formulation of Example 3 Ingredient % epoxy phenolnovolac 71.8 polyvinyl formal resin 5.0 bisphenol A diglycidyl ether(DGEBA) 9.9 540 eqWt Solid epoxy resin 6.0 dicyandiamide (DICY) 4.56-(2-(2-methyl-1H-imidazol-1-yl)ethyl)- 2.7 1,3,5-triazine-2,4-diaminepigment 0.1

A pre-preg was prepared from the epoxy resin formulation of Example 3 asfollows: A carbon fibre fabric (2×2 twill weave; areal weight of 200gsm) manufactured from a 3 k fibre (e.g., SM T300 3K from Toray®) wasimpregnated with the epoxy resin formulation of Example 3 to obtain aprepreg with a resin content of 38%. The pre-preg was used to make an8-ply 0/90° laminate which was then subjected to a 5 minute cure at acuring temperature of 160° C. The curing was performed in asteel-matched die tool pre-heated to the curing temperature. Theresulting laminate was tested by DMA following ASTM 7028-07, and foundto exhibit a Tg of about 170° C.

The viscosity of the resin formulation of Example 3 was analyzed asdescribed above. The formulation according to Example 3 exhibits a phaseangle of between about 74° and about 84° when heated from 20° C. to 60°C. Additional shear properties of the resin formulation of Example 3 areprovided in Table 15, below.

Example 4

An epoxy resin formulation according to Table 11 below was prepared bymixing the first three ingredients at 170° C. for two hours under lowshear. The mixture was cooled to 50° C., followed by the addition of theremainder of ingredients. The resulting mixture was mixed for 10minutes.

TABLE 11 Epoxy resin formulation of Example 4 Ingredient % bisphenol Adiglycidyl ether (DGEBA) 53.32 tetrafunctional epoxy resin 32.36polyethersulfone 4.20 dicyandiamide (DICY) 6.301-(cyanoethyl)-2-ethyl-4-methylimidazole 3.82

A pre-preg was prepared from the epoxy resin formulation of Example 4 asfollows: A carbon fibre fabric (2×2 twill weave; areal weight of 200gsm) manufactured from a 3 k fibre (e.g., SM T300 3K from Toray®) wasimpregnated with the epoxy resin formulation of Example 4 to obtain aprepreg with a resin content of 38%. The pre-preg was used to make an8-ply 0/90° laminate which was then subjected to a 5 minute cure at acuring temperature of 160° C. The curing was performed in asteel-matched die tool pre-heated to the curing temperature. Theresulting laminate was tested by DMA following ASTM 7028-07, and foundto exhibit a Tg of about 160° C.

The viscosity of the resin formulation of Example 4 was analyzed asdescribed above. The formulation according to Example 4 exhibits a phaseangle of between 70° and 87° when heated from 20° C. to 60° C.Additional shear properties of the resin formulation of Example 4 areprovided in Table 15, below.

Example 5

An epoxy resin formulation according to Table 12 below was prepared bymixing the first three ingredients at 170° C. for two hours under lowshear. The mixture was cooled to 50° C., followed by the addition of theremainder of ingredients. The resulting mixture was mixed for 10minutes.

TABLE 12 Epoxy resin formulation of Example 5 Ingredient % bisphenol Adiglycidyl ether (DGEBA) 39.51 tetrafunctional epoxy resin 50.13polyvinyl formal resin 3.30 dicyandiamide (DICY) 4.40 substituted ureacatalyst 2.65

A pre-preg was prepared from the epoxy resin formulation of Example 5 asfollows: A carbon fibre fabric (2×2 twill weave; areal weight of 200gsm) manufactured from a 3 k fibre (e.g., SM T300 3K from Toray®) wasimpregnated with the epoxy resin formulation of Example 5 to obtain aprepreg with a resin content of 38%. The pre-preg was used to make an8-ply 0/90° laminate which was then subjected to a 5 minute cure at acuring temperature of 160° C. The curing was performed in asteel-matched die tool pre-heated to the curing temperature. Theresulting laminate was tested by DMA following ASTM 7028-07, and foundto exhibit a Tg of about 178° C.

The viscosity of the resin formulation of Example 5 was analyzed asdescribed above. The formulation according to Example 5 exhibits a phaseangle of between 70° and 87° when heated from 20° C. to 60° C.Additional shear properties of the resin formulation of Example 5 areprovided in Table 15, below.

Comparative Example 1

The formulation prepared in accordance with Example 8 of WO 2017/030988was recreated, and included the formulation recited in Table 13:

TABLE 13 Epoxy resin formulation of Comparative Example 1 Ingredient %(wt) epoxy phenol novolac 61.30 bisphenol A diglycidyl ether (DGEBA)30.62 dicyandiamide (DICY) 4.38 1-(cyanoethyl)-2-ethyl-4-methylimidazole2.65 succinic acid 0.95 pigment 0.10

A pre-preg was prepared from the epoxy resin formulation of ComparativeExample 1 as follows:

A carbon fibre fabric (2×2 twill weave; areal weight of 200 gsm)manufactured from a 3 k fibre (e.g., SM T300 3K from Toray®) wasimpregnated with the epoxy resin formulation of Comparative Example 1 toobtain a prepreg with a resin content of 38%. The pre-preg was used tomake an 8-ply 0/90° laminate which was then subjected to a 5 minute cureat a curing temperature of 160° C. The curing was performed in asteel-matched die tool pre-heated to the curing temperature. Theresulting laminate was tested by DMA following ASTM 7028-07, and foundto exhibit a Tg of about 155° C.

The viscosity of the resin formulation of Comparative Example 1 wasanalyzed as described above. The formulation according to ComparativeExample 1 did not exhibit a phase angle of between 70° and 87° whenheated from 20° C. to 60° C. Additional shear properties of the resinformulation of Comparative Example 1 are provided in Table 15, below.

Comparative Example 2

A formulation was prepared in accordance with the examples of WO2014/096435, and included the formulation recited in Table 14:

TABLE 14 Epoxy resin formulation of Comparative Example 2 Ingredient %bisphenol A diglycidyl ether (DGEBA) 64.65 epoxy phenol novolac 18.79phenoxy resin 3.06 dicyandiamide (DICY) 9.00 substituted urea catalyst4.50

A pre-preg was prepared from the epoxy resin formulation of ComparativeExample 2 as follows:

A carbon fibre fabric (2×2 twill weave; areal weight of 200 gsm)manufactured from a 3 k fibre (e.g., SM T300 3K from Toray®) wasimpregnated with the epoxy resin formulation of Comparative Example 2 toobtain a prepreg with a resin content of 38%. The pre-preg was used tomake an 8-ply 0/90° laminate which was then subjected to a 5 minute cureat a curing temperature of 160° C. The curing was performed in asteel-matched die tool pre-heated to the curing temperature. Theresulting laminate was tested by DMA following ASTM 7028-07, and foundto exhibit a Tg of between about 110° C. and 120° C.

The viscosity of the resin formulation of Comparative Example 2 wasanalyzed as described above. While the formulation according toComparative Example 2 reaches a phase angle of between 70° and 87° whenat some point in the range of 20° C. to 60° C., the phase angle is notbetween 70° and 87° in the entire 20° C. to 60° C. range. Additionalshear properties of the resin formulation of Comparative Example 2 areprovided in Table 15, below.

TABLE 15 Shear Properties of the resin formulations of the Examples at20° C. Phase n*/Pa · s G*/Pa G′/Pa G″/Pa angle/° Example 1 1,740,00010,913,750 2,519,250 10,623,750 76.71 Example 2 3,900 24,511 7,79623,235 71.45 Example 3 413,500 2,598,124 325,400 2,577,666 82.81 Example4 1,650 12,635 3,519 12,135 73.83 Example 5 47,170 366,725 66,030360,731 79.62 Compar- 214,650 1,348,438 118,740 1,343,200 84.95 ative 1Compar- 3,232,625 20,311,250 7,170,999 19,001,250 69.39 ative 2

Prospective Example

A vinyl hybrid formulation according to one of Tables 16 or 17 belowwill be prepared by mixing (for example, by first mixing theresins/copolymer followed by addition of the curative).

TABLE 16 First vinyl hybrid resin formulation of Prospective ExampleIngredient % Vinyl hybrid hot melt resin 60%-80% Vinyl hybrid liquidresin 15%-25% Polyvinylformal resin, e.g., vinylec K 4%-7% Peroxyester1.5%-2.2%

TABLE 17 Second vinyl hybrid resin formulation of Prospective ExampleIngredient % Vinyl hybrid hot melt resins (e.g., more than one, 54%-66%in combination) Vinyl hybrid liquid resin 25%-35%Polybutylacrylate-co-methylmethacrylate copolymer 4.5%-7.5% Peroxyester1.5%-2.2%

Pre-pregs will be prepared from the vinyl hybrid resin formulations ofthe Prospective Example as follows:

A carbon fibre fabric (2×2 twill weave; areal weight of 200 gsm)manufactured from a 3 k fibre (e.g., SM T300 3K from Toray®) will beimpregnated with the vinyl hybrid resin formulation to obtain a prepregwith a resin content of approximately 38%. The pre-preg will be used tomake an 8-ply 0/90° laminate which will then be subjected to a curing atan adequate curing temperature. The curing is expected to be performedin a steel-matched die tool pre-heated to the curing temperature.

It is expected that the vinyl hybrid formulations will exhibit a glasstransition temperature (Tg) from about 130° C. to about 200° C. whencured, a phase angle of between, 70° and 85° when heated from 20° C. to60° C. It is also expected that the vinyl hybrid formulations willexhibit a cure conversion of at least 95% when cured for a duration ofno more than 10 minutes at a temperature of no more than 10° C. abovethe Tg of the curable resin when cured.

1-31. (canceled)
 32. A curable resin comprising at least onethermosetting resin, at least one curative and at least onethermoplastic additive in a ratio such that the curable resin exhibits:(i) a glass transition temperature (Tg) from about 130° C. to about 200°C. when cured; (ii) a cure conversion of at least 95% when cured for aduration of no more than 10 minutes at a temperature of no more than 10°C. above the Tg of the curable resin when cured; (iii) a phase angle ofbetween between 50° and 87°, and preferably between 70° and 85°, whenheated from 20° C. to 60° C.; and (iv) optionally, a complex modulus ofbetween about 100 Pa·s and about 10,000,000 Pa·s between 20 and 60° C.33. The curable resin according to claim 32, wherein the curable resinexhibits a cure conversion of at least 95% when cured for a duration ofno more than 10 minutes at a temperature between about 120° C. and about175° C.
 34. The curable resin according to claim 32, wherein thethermosetting resin is selected from epoxy resin(s), resins comprisingvinyl groups and mixtures thereof.
 35. The curable resin according toclaim 32, wherein the at least one curative is present in an amount offrom about 1 wt % to about 10 wt %.
 36. The curable resin according toclaim 32, wherein the thermosetting resin is selected from bifunctionalor multifunctional epoxy resin(s) and wherein the curative is selectedfrom imidazole curatives, (poly)amine curatives, substituted (poly)aminecuratives, and mixtures thereof.
 37. The curable resin according toclaim 36, wherein the curative is at least one compound selected from6-(2-(2-methyl-1H-imidazol-1-yl)ethyl)-1,3,5-triazine-2,4-diamine,1-((2-methyl-1H-imidazol-1-yl)methyl)naphthalen-2-ol,3-(2-phenyl-1H-imidazol-1-yl)propanenitrile,(2-phenyl-1H-imidazole-4,5-diyl)dimethanol,bis(2-ethyl-5-methyl-1H-imidazol-4-yl)methane,1-(cyanoethyl)-2-ethyl-4-methylimidazole,6-[2-(2-ethyl-4-methylimidazol-1-yl)ethyl]-1,3,5-triazine-2,4-diamine,1,3-diaminobenzene, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulphone (4,4′ DDS), 3,3′-diaminodiphenyl sulphone (3,3′ DDS),bis(4-amino-3,5-dimethylphenyl)-1,4-diisopropylbenzene,bis(4-aminophenyl)-1,4-diisopropylbenzene,4-chlorophenyl-N,N-dimethyl-urea, 3,4-dichlorophenyl-N,N-dimethyl-urea,2,6- and 2,4-toluene bis dimethyl urea, dicyandiamide, and mixturesthereof.
 38. The curable resin according to claim 36, wherein saidcurative is a mixture of at least one imidazole curative and at leastone (poly)amine or substituted (poly)amine curative.
 39. The curableresin according to claim 38, wherein said diamine curative isdicyandiamide.
 40. The curable resin according to claim 32, wherein saidcurative is a solid curative or a mixture of solid curatives.
 41. Thecurable resin according to claim 32, wherein the thermosetting resin isa bifunctional or multifunctional epoxy resin, or a mixture ofbifunctional or multifunctional epoxy resins.
 42. The curable resinaccording to claim 41, wherein the difunctional or multifunctional epoxyresin(s) are selected from resin based on glycidyl ethers of phenol andcresol epoxy novolacs, glycidyl ethers of phenol-aldehyde adducts,aromatic epoxy resins, aliphatic triglycidyl ethers, dialiphatictriglycidyl ethers, aliphatic polyglycidyl ethers, epoxidised olefins,triglycidyl aminophenols, aromatic glycidyl amines, heterocyclicglycidyl imidines and amides, glycidyl ethers, fluorinated epoxy resins,N,N,N′,N′-tetraglycidyl diamino diphenylmethane (TGDDM) andN,N,N′,N′-tetraglycidyl-m-xylenediamine, or any combination thereof; andwherein said difunctional epoxy resins are selected from diglycidylether of bisphenol F (DGEBF), diglycidyl ether of bisphenol A (DGEBA),diglycidyl ether of dihydroxy naphthalene, or any combination thereof.43. The curable resin according to claim 42, wherein the difunctional ormultifunctional epoxy resin(s) consist essentially of an epoxy phenolnovolac (EPN) resin in combination with an additional difunctional ormultifunctional epoxy resin.
 44. The curable resin according to claim41, wherein the additional difunctional or multifunctional epoxy resinis selected from bisphenol A epoxy resins, preferably DGEBA.
 45. Thecurable resin according to claim 32, wherein the thermosetting resin isselected from resins comprising vinyl groups and wherein the curative isselected from peroxide curatives.
 46. The curable resin according toclaim 45, wherein the curative is at least one compound selected fromdibenzoyl peroxide, di-t amyl peroxide, di-t butyl peroxide, dicumylperoxide, t-butyl peroxy-2-ethylhexyl carbonate, t-amylperoxy-2-ethylhexyl carbonate, di-(4-t-butylcyclohexyl)-peroxydicarbonate, t-butyl peroxybenzoate, t-butylperoxyacetate, t-butyl peroxy-2-ethylhexanoate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butyl monoperoxymaleate, t-amylperoxybenzoate, ethyl-3,3-di(t-butylperoxy) butyrate,1,1-di-(t-butylperoxy) cyclohexane,1,1-di-(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di-(t-amylperoxy)cyclohexane, 2,5-dimethyl-2,5-di-(2-ethylhexanoylperoxy)hexane,tert-butylperoxy isopropyl carbonate, 2,2-bis(tert-butylperoxy)butane,tert-butyl peracetate and mixtures thereof.
 47. The curable resinaccording to claim 32, wherein the curable resin comprises: at least onethermosetting resin selected from difunctional or multifunctional epoxyresin(s); from about 1 wt % to about 15 wt %, preferably from about 1 wt% to about 10 wt %, of at least one curative selected from imidazolecuratives, (poly)amine curatives and substituted (poly)amine curatives;and from about 2 wt % to about 10 wt %, preferably from about 2 wt % toabout 8 wt %, of at least one thermoplastic additive.
 48. The curableresin according to claim 32, wherein the curable resin comprises: atleast one thermosetting resin selected from vinyl ester resin(s) orurethane acrylate resin(s); from about 1 wt % to about 15 wt %,preferably from about 1 wt % to about 10 wt %, of at least one curativeselected from organic acyl peroxide curatives, peroxy carbonatecuratives, peroxyester curatives, peroxyketal curatives, and(alkyl)peroxide curatives; and from about 2 wt % to about 10 wt %,preferably from about 2 wt % to about 8 wt %, of at least onethermoplastic additive.
 49. The curable resin according to claim 32,wherein the thermoplastic additive is present in an amount of from about2 wt % to about 10 wt %.
 50. The curable resin according to claim 32,wherein the thermoplastic additive is selected frompolyarylethersulfones, polysulfones, polyvinylformals,polymethylmethacrylates, polyimides, polyetherimides, phenoxy resins,modified butadiene nitrile polymers and polyamides.
 51. The curableresin according to claim 50, wherein the thermoplastic additivecomprises a polyvinylformal resin.
 52. The curable resin according toclaim 50, wherein the thermoplastic additive comprises a phenoxy resin.53. The curable resin according to claim 50, wherein the thermoplasticadditive comprises a polyarylethersulfone resin.
 54. The curable resinaccording to claim 32, wherein the curable resin exhibits an epoxyequivalent weight of at least about 150 g/mol, preferably in the rangeof from about 150 to about 250 g/mol.
 55. A pre-preg of fiber-reinforcedcurable composite material, wherein said pre-preg comprises at least onelayer of reinforcing fibers impregnated with a curable resin accordingto claim
 32. 56. The pre-preg according to claim 55, wherein thepre-preg comprises reinforcing fibers in an amount of from about 20% toabout 70% reinforcing fibers, for example from about 45% to about 60%,wherein the percentages refer to the volume percent of the fiber bytotal volume of the pre-preg.
 57. The pre-preg according to claim 55,wherein said reinforcing fibers exhibit a tow size of at least 12,000filaments per tow and/or said at least one layer of reinforcing fibersis a fabric which exhibits an areal weight of at least about 150 g/m².58. The pre-preg according to claim 55, wherein said reinforcing fibersare continuous filaments, preferably wherein said reinforcing fibers arein the form of untwisted bundles of continuous filaments.
 59. Thepre-preg according to claim 55, wherein the thickness of the pre-preg isfrom about 150 μm to about 1500 μm, for example from about 150 μm toabout 500 μm.
 60. A process for the production of a molded article froma plurality of pre-pregs, the process comprising: (a) disposing apre-preg into or onto a mold; (b) optionally repeating step (a) at leastonce to dispose one or more further pre-pregs into or onto said mold;and (c) thermally curing the plurality of pre-pregs; wherein saidpre-preg is a material as defined in claim
 24. 61. A process accordingto claim 60, wherein said thermal curing is effected while the pre-pregsare compressed in a mold cavity, preferably an isothermally heated moldcavity.
 62. A process according to claim 60 wherein thermal curing isconducted at a cure temperature in the range of from about 120° C. toabout 175° C., and wherein the plurality of pre-pregs is held at saidcure temperature for a duration of no more 10 minutes.